So some Trump enablers in the Senate are using their investigative powers to bully the author of the Trump-Russia dossier. Alarming, of course, but unsurprising: this crew (namely, Congressional Republicans) have been abusing their investigative powers for years, largely under the radar of the mainstream media. Off the top of my head, I can think of several conservative scandals du jour in which Congressional Republicans abused their investigative powers to target their political enemies for years: Benghazi, Planned Parenthood "baby parts", "IRS targeting", and several others come to mind.
This is obviously a very useful tactic politically. For one, you can use it to tie up your political enemies in subpoena responses and legal fees. Every hour and dollar Planned Parenthood spent responding to the "baby parts" committee was an hour/dollar spent not doing the things that Congressional Republicans don't like (namely, expanding access to abortion and trying to elect Democrats), and every hour and dollar that Lois Lerner spent responding to inquiries in the obviously fake IRS targeting scandal was an hour/dollar spent not doing a thing Congressional Republicans don't like (namely, collecting taxes and enforcing the tax laws).
Additionally, Congressional investigations carry with them a certain imprimatur of legitimacy, as the media and the general public largely haven't caught on to the fact that Congressional Republican investigations are fake. They presume that members of Congress act in good faith when they subject people and institutions to investigation, and respond to these investigations accordingly. It's therefore profoundly stigmatizing and delegitimizing when Congress investigates you. Even when nothing comes of these investigations (and nothing ever does, because they're fake), the targets are significantly harmed.
Finally, these fake investigations fuel the parallel conservative media world. Fox News, Breitbart, etc. can cover them endlessly. When they don't go anywhere (and they never do, because they're not real), conservative media can blame the Obama administration, the deep state, etc. for covering up Very Serious Wrongdoing. It's rocket fuel for the conservative media culture of grievance and conspiracy-mongering.
While the misuse of investigative powers to target political enemies is to a certain extent driven by the unique pathologies of the contemporary Republican Party, I think the misuse of investigative powers for political purposes is ultimately a structural problem. Investigative powers--subpoenas, the contempt power, etc--are both really politically useful and really intrusive. This combination means that the temptation to use them for nefarious political purposes, and by using them abuse the rights of citizens, will always be there. It's why, in other contexts, there are strong Constitutional and legal protections against their misuse for political purposes. For instance, the Constitution has a warrant requirement for investigatory searches and seizures, which separates investigative powers between politically accountable prosecutors and politically insulated judges. At the state level, there's significant (albeit imperfect) vertical and horizontal separation of powers between political actors (namely, the governor and the legislator) and actors with investigatory power (state attorneys general and district attorneys). All of this serves to limit potential abuse of investigatory power for political purposes. But few of these protections are present when it comes to Congressional investigations.
Ultimately, I think this problem is just an unavoidable result of giving investigatory powers to an entity that's inherently political, like a legislature. Fortunately, the solution is simple: the Congressional investigatory power is an extra-Constitutional inferred power (look at Article 1! There's nothing about investigations in there!). Courts have given it, and courts can take it away. The victims of abusive Congressional investigations should challenge subpoenas, etc. in court, and courts should skeptically review the bad-faith actions of Congressional investigators.